Introduce a new attribute to externally_connectable,
accepts_tls_channel_id.  When sites are allowed to connect to an
extension, and specify include_tls_channel_id in their
chrome.runtime.connect or chrome.runtime.sendMessage options,
and the extension sets the accepts_tls_channel_id attribute,
automatically annotate the TLS channel ID as an attribute of the
MessageSender given to the onConnectExternal handler.

BUG=259097

Review URL: https://codereview.chromium.org/23002007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227722 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227722